A Dynamic Robotic Actuator with Variable Physical Stiffness and Damping

Abstract

This study is part of research aiming at increasing the range of dynamic tasks for teleoperated field robotics in order to allow operators to use the full range of human motions without being limited by the dynamics of the robotic manipulator. A new variable impedance actuator (VIA) was designed, capable of reproducing motions through teleoperation from precise positioning tasks to highly dynamic tasks. The design requirements based on previous human user studies were a stiffness changing time of 50 ms, a peak output velocity of 20 rad/s and variable damping allowing to suppress undesired oscillations. This is a unique combination of features that was not met by other VIAs. The new design has three motors in parallel configuration: two responsible for changing the VIA's neutral position and effective stiffness through a sliding pivot point lever mechanism, and the third acting as variable damper. A prototype was built and its performance measured with an effective stiffness changing time of 50 to 120 ms for small to large stiffness steps, nominal output velocity of 16 rad/s and a variable damper with a damping torque from 0 to 3 Nm. Its effective stiffness range is 0.2 to 313 Nm/rad. This concludes that the new actuator is particularly suitable for highly dynamic tasks. At the same time, the new actuator is also very versatile, making it especially interesting for teleoperation and human-robot collaboration.